The present invention refers generally to spiral heat exchangers for various purposes. More specifically, the invention refers to a spiral heat exchanger for recovering heat from problematic fluids, such as sludge. In particular, the present invention refers to a spiral heat exchanger including a central cylinder and at least two spiral sheets extending from the cylinder along a respective spiral-shaped path around a common center axis and forming at least a first spiral-shaped flow channel for a first medium and a second spiral-shaped flow channel for a second medium, wherein the cylinder extends around the center axis and forms an inner space within the cylinder, and wherein the cylinder includes a front end, a rear end, at least a first lateral opening communicating with the first flow channel and at least a second lateral opening communicating with the second flow channel.
Such a spiral heat exchanger is disclosed in SE 112 656. This document discloses one embodiment comprising a central cylinder. The cylinder is formed in one piece with an end plate. Two separate headers are provided in the inner space of the cylinder for the fluid communication with a respective spiral flow channel.
Conventionally, spiral heat exchangers are manufactured by means of a winding operation. The two sheets are welded together at a respective end, wherein the welded joint will be comprised in a center portion of the sheets. Alternatively, one single sheet is used for the manufacturing of the heat exchanger. Distance members, having a height corresponding to the width of the flow channels, are attached to the sheets. Before being wound, the center portion of the sheet or sheets is introduced into a gap of a retractable mandrel. Then the mandrel is rotated, wherein the sheets are wound to form the spiral element of the sheets. After retraction of the mandrel, two inlet/outlet channels are formed in the center of the spiral element. The two channels are separated from each other by the center portion of the sheets. The side ends of the spiral element are processed, wherein the spiral flow channels may be laterally closed at the two side ends in various ways. Typically, a cover is attached to each of the ends. One of the covers may include two connection pipes extending into the center and communicating with a respective one of the two flow channels. At the radial outer ends of the spiral flow channels a respective header is welded to form an outlet/inlet member to the respective flow channel.
One problem with this conventional spiral heat exchanger is the relatively complex manufacturing work needed for the mounting of the connection pipes extending from the center of the spiral heat exchanger. In particularly, the problem is related to the difficulty to achieve a proper and desired position for the two connection pipes and the headers at the periphery of the spiral element. It is frequently important that the headers are located at the top of the spiral element, and also that the connection pipes are positioned along a vertical plane. Furthermore, in case of a heat exchanger designed for receiving sludge as one of the media, it is also important that one connection pipe forming the sludge outlet is located beneath the other connection pipe forming a water inlet. These requirements imply that the center portion should be at least approximately horizontal. In order to obtain such a position of the connection pipes, the outer ends of the sheets frequently need to be cut after the winding operation.
CH 539 257 discloses another spiral heat exchanger element which is mounted in a cylindrical vessel. The heat exchanger element includes a central cylinder and two spiral sheets extending from the cylinder along a respective spiral-shaped path around a center axis. The spiral sheets form a first spiral-shaped flow channel for a first medium and a second spiral-shaped flow channel for a second medium. The cylinder extends around the center axis and forms an inner space in the cylinder. The cylinder includes a first opening and a second opening, which both communicate with one and the same of flow channels.